High-frequency gas discharge device



March 4, 1952 w. M. WEBSTER ET AL 2,583,065

. HIGH-FREQUENCY GAS DISCHARGE DEVICE Filed Sept. 20, 1950 7 NEY Patented Mar. 4, 1952 HIGH- FREQUENCY GAS DISCHARGE DEVICE William M. Webster, Edward 0. Johnson, and Louis Malter, Princeton, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application September 20, 1950, Serial No. 185,746

14 Claims.

Our present invention relates to an electron discharge device of the type in which an ionizable medium is employed to support a discharge. More particularly our invention relates to such a device in which a control electrode may continuously control or modulate the current through the device at a very high frequency rate.

In the co-pending sole application of E. 0. Johnson filed simultaneously herewith, Serial Number 185,745, are described and claimed gas discharge devices which can be used in applications in which gas tubes heretofore were unsatisfactory or could not be used. As pointed out in said co-pending application such gas discharge devices may be used to drive loads requiring continuous radio frequency modulation in the place of vacuum tubes. When so used several relatively costly circuit components or stages may be dispensed with. For example, a voice coil may be directly driven by one of the devices of said co-pending application, thereby replacing, in addition to a vacuum tube amplifier, a relatively costly transformer. Nevertheless, for certain application in the very high frequency range the utility of such devices may be increased if the frequency response thereof is improved.

It is, therefore, a principal object of our invention to provide a gas discharge device capable of very high frequency operation.

Another object of our invention is the provision of gas discharge device wherein a cathode, grid and anode are immersed in plasma created by two auxiliary cathodes and in which the grid 'modulates the current flow between main cathode and anode at a frequency of 100 megacycles or more.

Yet another object is the provision of such a device in which two intense ionizing discharges are formed, one being directed toward the grid past the cathode and the other being directed toward the grid through the anode.

.their ends by means of straps 24.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims. The invention itself will be best understood by reference to the following description taken in connection with the accompanying drawing in which:

Figure 1 is a transverse sectional view of a gas discharge device constructed in accordance with our invention; and I Figure 2 is a sectional view thereof through the line 2-2 of Figure 1.

Referring now to the drawing in detail, gas discharge device I!) comprises a gas tight envelope ll only partially indicated in Figure 2. The device is provided with the usual stem (not shown) through which the lead-in conductors are sealed in the usual manner. The electrode assembly is supported by means of the conductors within the envelope as indicated. Between upper and lower insulating members I 3 and M are mounted a main cathode l5, a control electrode or grid l6 and a main anode l1. Cathode I5 is the usual oxide coated sleeve type cathode having a non-inductive type heater I8 extending therein, the leads of which are each connected to supporting conductors I9, 20; the cathode also being connected to conductor I9. The upper end of main cathode I5 is crimped in the well known manner to lock the same in place between the insulating members.

Control electrode or grid l6 comprises a plurality of parallel spaced wires 2l which extend into holes or recesses formed in insulating members l3 and I4. Adiacent each of their ends, grid wires 2| are interconnected by a pair of straps 22. p v

Main anode l1 comprises a plurality of spaced parallel wires 23. As in the case of grid wires 2|, main anode wires 23 are interconnected at The upper and lower ends of main anode wires 23 extend into holes or recesses formed in insulating members l3 and I4 and may be crimped in order to lock the anode in place. The end wires 23 depend below lower insulating member l4 and are conveniently interconnected by conductive member 25 while one of said wires may be connected to supporting conductor 26.

Main cathode I 5, control electrode [6 and main anode I! are substantially enclosed by a pair of oppositely disposed members 21, 28 which form an open ended enclosure. Members 21, 28 may be sheet metal such as nickel and form an enclosure and shield against undesirable electron and ion paths. As most clearly shown in Figure 1, control electrode [6 extends across the space between members 21, 28 and, as indicated, may be mechanically and electrically connected thereto by straps 22. Members 21 and 23 are each supported between insulating members l3 and I 4 by means of rods or wires 29 connected thereto in a suitable manner as, for example, by welding. Rods or wires 29 extend above and below insulating members l3 and I4; one of which being connected to supporting conductor 30.

As shown most clearly in Figure 1 members 21 and 28 extend beyond both the main cathode and the main anode. Adiacent each of the open ends of said members 21 and 2B are mounted means for creating and sustaining a plasma which extends continuously and normally without interruption between main cathode l and main anode I! through control electrode or grid [8.

As is generally understood, the plasma in gas discharge devices contains positive and negative particles, that. is ions and electrons, which are equivalent in number or substantially equal. Both control electrode [5 and main anode I! normally interfere with the difiusion of the plasma to a negligible extent.

Adjacent the open end of the enclosure formed by members 21 and 28 near main cathode I5 is mounted a cylindrical focusing electrode 31 supported between insulating members l3, M by means of wires or rods 32. One of the wires 32 is connected to supporting conductor 33. Auxiliary cathode 34 may be an oxide coated sleeve type cathode having heater 35 extending therein. Auxiliary cathode 34 is conveniently mounted concentric with focusing electrode 3i; the latter having a slot or elongated opening 36 formed therein opening toward main cathode l5.

Between slot 36 and main cathode I5 is mounted auxiliary anode 3'! comprising a pair of spaced parallel wires interconnected above insulating member l3 by means of strap 38. The wires of auxiliary anode 31 are each located outside of the direct path between slot 36 and main cathode !5.

Similarly, cylindric focusin electrode 39 and concentric auxiliary cathode 40 are mounted adjacent the other open end of the enclosure formed by members 21 and 28; auxiliary cathode 40 having heater 44 extending therein. Focusing electrode 39 also has a slot 4| formed therein opening toward main anode I'I. Auxiliary anode 42 is similar to auxiliary anode 3! and is disposed with its wires outside of and on both sides of the direct path between auxiliary cathode 4D and main anode l1. Auxiliary anode 42 comprises wires which extend above upper insulating member 13 where they are conductively connected by strap 43.

Gas discharge device In is processed in the usual manner. It is exhausted and gettered and then filled with a suitable ionizable medium. Any of the well known gases or vaporizable materials known in the gas discharge art may be utilized, though we prefer the rare gases and in particular helium or argon. The gas pressure may vary from approximately 100 microns to several millimeters of mercury. In the device now being described for the purpose of illustrating our invention we utilized helium at a pressure of 750 microns.

The parallel spaced wires of control electrode is and main anode ll form in effect apertured electrodes. It is not essential that they be constructed in the manner illustrated though we have found that the construction shown is advantai in the medium. In one of such devices In which were constructed, the space between the wires of each of electrodes l6 and I! is 1.5 millimeters.

We preferably operate device ill with each of the focusing electrodes connected to its auxiliary cathode although the focusing electrodes may be operated at potentials different from that of the auxiliary cathodes. The focusing electrodes and auxiliary cathodes are connected to the negative side of a source of potential through a limiting resistance while the auxiliary anodes are connected to the positive side thereof. The main cathode and the auxiliary anodes are conveniently at the same potential and may be tied to ground. In series between main cathode l5 and main anode I1 is a second source of potential. This is the load or main circuit and a load impedance is connected between the main anode and the second source. The control electrode or grid is con-- nected to the negative side of a third source of potential the positive side of which is connected to the main cathode and serves as the source of biasing potential. A signal source may be connected in series between the negative side of the bias source and the control electrode.

As indicated in the drawing, heaters 35 and 44 are each provided with two leads. Heater 35 has leads 45, 46 connected thereto while heater 44 has leads 41, 48 connected thereto. A suitable source of heater current is connected between each of the heater leads to provide the heaters with the usual current at approximately six volts.

The sources of potential are so chosen that the potential between the auxiliary cathodes and the auxiliary anodes is great enough to result in an ionizin discharge therebetween while the potential between main cathode l5 and main anode I1 is less than that required to cause an ionizing discharge between them. With an atmosphere of helium at a pressure of 1750 microns we utilized approximately 50 volts between the auxiliary cathodes and anodes. The potential between the main cathode and anode may vary from 0 to 25 volts. The bias voltage on the control electrode may vary from about a volt to approximately twenty volts negative with respect to the main cathode.

Device it! may be used in place of vacuum or hard tubes to effect modulation at frequencies of megacycles or better. When so used, device I!) delivers as much as 100 milliamperes of current with extremely low anode potentials and makes possible elimination of components such as transformers or the like which are required when vacuum tubes are utilized.

The underlying principles which are believed applicable to such an invention are pointed out in detail in such co-pending application. However, it may be pointed out that in our present device with the main cathode and anode connected across a source of potential and the auxiliary electrodes disconnected from this source, device It! will have characteristics similar to those of the usual thyratron. That is, by making the control electrode more or less negative it will stand Q Q1 event e fo macurrent paths in device I0.

tion of a discharge for various anode potentials. For a given anode potential, as the grid or control electrode is made less negative a point is reached where breakdown occurs and an ionizing discharge forms. The potential available to the anode must be approximately equal to the ioni,- zation potential of the medium in order for a discharge between the cathode and anode to appear. .As in the case of the usual thyratron, the control electrode is surrounded by a sheath which, for an electric negative to the cathode, is a positive ion sheath. The field from the control electrode terminates in its sheath and is powerless to affect the plasma for all practical purposes. After the appearance of a plasma between the cathode and anode, if the grid is made more negative in an attempt to modulate the current flowing between the anode and cathode, the grid sheath momentarily expands. The constriction of the plasma in the grid openings results in an increase in the voltage drop and a consequent speeding up of the electrons. This in turn results in more intense ionization and the grid sheath very rapidly shrinks to almost its original thickness. As a result, even though the grid is made more and more negative the total effect is negligible.

On the other hand, with the auxiliary electrodes connected to their source of potential two visible discharges appear and the main electrodes are bathed in plasma. The plasma can normally diffuse freely through the openings or apertures in the control electrode and main anode. The plasma in the region between the grid and main cathode is sustained primarily from auxiliary cathode 34 while the plasma in the grid-main anode region is sustained pri marily by auxiliary cathode d0. It is no longer necessary for the potential between the main cathode and main anode to exceed the ionization potential for such a potential to appear between the main cathode and the main anode as may result in a self-sustaining discharge between them. Now the excursions of the control electrode or grid do not aiiect the auxiliary or ionization currents since the grid does not extend across either of the auxiliary or ionization One of the ionization current paths is between auxiliary cathode 34 and auxiliary anode 37. The otherionization current path lies between auxiliary cathode 4D and auxiliary anode 42.

When control electrode or grid l6 swings sufiiciently negative to render the main or load circuit through device It non-conductive, the grid sheath extends across and closes the openings of the grid and prevents the passage of electrons from the main cathode therethrough. Since the plasma is being sustained by the auxiliary or ionization currents which continue to flow there is no tendency for the plasma to oppose the action of the grid sheath and the grid may function as the grid of a vacuum tube does. Thus, as the grid is modulated and made more or less negative the grid sheath follows these variations.

The plasma which normally extends continuously and without interruption between main cathode l5 and main anode I! through control electrode H5 is believed to function as a conductor for the main or load currents. is modulated the streams of plasma in the grid openings are contracted and then permitted to expand. Just as in the case of a common conductor, it appears that as its cross-sectional As the grid modulated at very high frequencies.

area is decreased, the conductance of the plasma streams also decreases.

ating and grid I6 at out off it is clear that the plasma in the grid-main anode region is de caying and is not being sustained in view of the blocking action of the grid sheath. Now as the grid is made more positive and the plasma may once again diifuse through the grid full conduction in the main or load circuit can not take place until the plasma diffuses through the grid and -re-establishes itself in the grid-anode region. This would limit the frequency of operation of device I!) to a frequency much lower than 100 megacycles. However, with both auxiliary cathodes operating this is not the case.

The plasma in the'region between the main anode l1 and grid 16 is sustained by the plasma which may always diifuse through the main anode and only the plasma extending through the grid openings is aifected by the excursions of "the control electrode. In view of the relatively short distances involveddevice It may be Furthermore, the plasma is now reestablished from sources on either side of the grid.

We have found by using the construction il lustrated, the plasma oscillations which appear in the operation of the usual gas discharge de vices do not appear in device ID or are of such a nature as not to affect the operation of the device. This is attributed to the fact that the focusing electrodes make it possible to obtain the required ionization while at the same time utilizing an extremely small amount of current in the auxiliaryor ionization circuits. As pointed out, limiting'resistances are connected in series be tween each of the auxiliary cathodes and its source and the auxiliary current may be as little as ten milliamperes or less. Even with so little current flowing the action of the focusing electrodes is such that an intense visible discharge appearsoutside of each of the slots 36 and M. It is believed apparent that if the auxiliary circuits also carried the main or load current the current passing therethrough would be measured in hundreds of 'amperes rather than merely in a few milliamperes. Under such conditions the plasma oscillations would appear greatly intensified and would seriously interfere with and limit the use of such a device.

In view of the action of the focusing electrodes in making it possible for such extremely small currents to flow in the auxiliary or ionization currents it is possible to use comparatively small and inexpensive sources to supply the necessary power. Also, in view of the small current involved in the ionization circuits, collection by any of the main electrodes of a small percentage of this current may be disregarded for all practical purposes.

It is believed obvious that though we have shown only one specific embodiment and have described our invention in connection therewith. an invention is subject to wide variations and modifications without departing from the spirit thereof. It is, therefore, intended to cover all such modifications which come within the scope of the appended claims.

We claim:

l. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a cathode and an anode mounted in spaced relation in said envelope, said anode having at least one opening formed therein, means for ionizing said medium and including a first auxiliary electrode located adjacent said cathode, and means for ionizing said medium and including a second auxiliary electrode located on the side of said anode away from said oathode.

2. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a cathode and an anode mounted in spaced relation in said envelope, said anode having at least one opening formed therein, means for ionizing said medium and located adjacent said cathode, and means for ionizing said medium and located on the side of said anode away from said cathode.

3. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a cathode and an anode mounted in spaced relation in said envelope, said anode having at least one opening formed therethrough, said opening being large compared to the mean free path of ions in said medium, means adjacent said cathode for ionizing said medium, and means on the side of said anode away from said cathode for ionizing said medium.

4. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a cathode and an anode mounted in spaced relation in said envelope, said anode comprising a plurality of parallel spaced wires, means on the side of said anode toward said cathode for ionizing said medium, and means on the side of said anode away from said cathode for ionizing said medium.

5. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a cathode and an anode mounted in spaced relation in said envelope, said anode comprising a plurality of parallel spaced wires, the spaces between said wires being large compared to the mean free path of ions in said medium. means on the side of said anode toward said cathode for ionizing said medium, and means on the side of said anode away from said cathode for ionizing said medium.

6. A gas discharge device, comprising .a gas tight envelope, an ionizable medium in said envelope, a cathode and an anode mounted in spaced relation in said envelope, a control electrode mounted intermediate said cathode and anode, said control electrode and said anode each having at least one opening formed therethrough, means on the side of said control electrode toward said cathode for ionizing said medium, and means on the other side of said control electrode for ionizing said medium.

'7. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a cathode, control electrode and an anode spaced in said envelope in that order, said control electrode and said anode each comprising a plurality of spaced wires, and means on both sides of said control electrode for ionizing said medium.

8. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a cathode, control electrode and an anode spaced in said envelope in that order, said control electrode and said anode each comprising a 8 plurality of spaced wires, the spaces between the wires of said control electrode and said anode being large compared to the mean free path of ions in said medium, and means on both sides of said control electrode for ionizing said medium.

9. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a thermionic cathode, a control electrode and a main anode spaced in that order in said envelope, an auxiliary cathode on the side of said control electrode toward said main cathode, and another auxiliary cathode on the side of said main anode away from said control electrode.

10. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a thermionic cathode, a control electrode and a main anode spaced in that order in said envelope, an auxiliary cathode on the side of said control electrode toward said main cathode, another auxiliary cathode on the side of said main anode away from said control electrode, and a plurality of auxiliary anodes at least one for each of said auxiliary cathodes.

11. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a thermionic cathode, a control electrode and a main anode spaced in that order in said envelope, said control electrode and said main anode each having at least one opening formed therethrough, an auxiliary cathode on the side of said control electrode away from said main anode, an auxiliary anode adjacent said auxiliary cathode and spaced therefrom, a focusing electrode intermediate said auxiliary cathode and auxiliary anode, another auxiliary cathode mounted on the side of said main anode away from said control electrode and spaced therefrom, another auxiliary anode adjacent said other auxiliary cathode, and a focusing electrode intermediate said other auxiliary cathode and said other auxiliary anode.

12. A gas discharge device, comprising a gas tight envelope, an ionizable medium in said envelope, a thermionic cathode, a control electrode and a main anode spaced in that order in said envelope, said control electrode and said main anode each comprising a plurality of parallel spaced wires, the spaces between said wires being large compared to the mean free path of ions in said medium, an auxiliary'cathode on the side of said control electrode away from said main anode, an auxiliary anode adjacent said auxiliary cathode and spaced therefrom, a focusing electrode intermediate said auxiliary cathode and auxiliary anode, another auxiliary cathode mounted on the side of said main anode away from said control electrode and spaced therefrom, another auxiliary anode adjacent said other auxiliary cathode, and a focusing electrode intermediate said other auxiliary cathode and said other auxiliary anode.

13. A gas discharge device comprising a gas tight envelope, an ionizable medium in said envelope, a pair of spaced apart members mounted in said envelope and forming an enclosure open at the ends thereof, a main cathode and a main anode mounted in spaced relation within said enclosure, a grid electrode extending across said enclosure between said main cathode and said main anode, a cylindrical focusing electrode substantially closing the end of said enclosure adjacent said main cathode, an ionization cathode within said focusing electrode, said focusing electrode having a slot formed therethrough opening toward said main cathode, another cylindrical focusing electrode having a slot formed therein and substantially closing the other end of said enclosure adjacent said main anode, and another ionization cathode within said other focusing electrode, the slot in said other focusing electrode opening toward said main anode.

14. A gas discharge device, comprising a gas tight envelope, an ionization medium in said envelope, a pair of spaced apart opposed elongated members forming an enclosure open at the ends 7 thereof, a main cathode and a main anode mounted in spaced relation within said enclosure, said main anode comprising a plurality of spaced apart wires, a control electrode comprising a plurality of spaced apart wires and extending across said enclosure intermediate said main cathode and said main anode and connected to said members, a cylindrical focusing electrode substantially closing the end of said enclosure adjacent said main cathode and having a slot formed therein opening toward said main cathode, an ionization cathode mounted in said focusing electrode and concentric therewith, an ionization anode outside of said focusing electrode and adjacent a path extending between said cathodes, another cylindrical focusing electrode substantially closing the end of said enclosure adjacent said main anode and having a slot formed therein opening toward said main anode, another ionization cathode mounted within said focusing electrode and concentric therewith, and another ionization anode intermediate said focusing electrode and said main anode.

WILLIAM M. WEBSTER.

EDWARD O. JOHNSON.

LOUIS MALTER.

REFERENCES CITED UNITED STATES PATENTS Name Date Lalewicz Aug. 23, 1949 Number 2,479,846 

